1. Field of the Invention
The invention relates to a small current sensor capable of detecting a change of a current flowing through a conductor with high precision.
2. Description of Related Art
Generally, as a method of measuring a control current for controlling a control device or the like, there is used a method of indirectly measuring the control current by detecting a gradient of a current magnetic field generated by the control current. Specifically, for example, four magneto-resistive elements such as giant magneto-resistive elements (hereinafter, referred to as GMR elements) exhibiting giant magneto-resistive effect are used to form a Wheatstone bridge, the Wheatstone bridge is arranged in the current magnetic field, and the gradient thereof is detected (for example, see U.S. Pat. No. 5,621,377).
As described above, by forming a Wheatstone bridge, influence of external noise (an interference magnetic field) or environmental temperature may be suppressed at relatively low level. Particularly, in the case where the characteristics of the four magneto-resistive elements are uniform, more stable detection property is obtainable.
In addition, there has been disclosed an example in which a change of an output voltage caused by environmental temperature or external noise is further reduced by providing a compensation current line (for example, see U.S. Pat. No. 5,933,003).
Further, in the view of increasing requirements for detecting a weaker current, a magneto-resistive element with high impedance and higher sensitivity is demanded. However, in the case where a Wheatstone bridge is configured by using a magneto-resistive element with high impedance and high sensitivity, a large offset output is likely to be generated or large variation in connection resistance is likely to occur. Therefore, it is difficult to adjust balance between four magneto-resistive elements configuring the Wheatstone bridge. Thus, the applicants have previously proposed a current sensor capable of detecting a current magnetic field of a current-to-be-detected with high sensitivity and high precision while adjustment of an offset voltage in a zero magnetic field is easily preformed (for example, see Japanese Patent No. 4360998).